This invention relates generally to fluorescent penetrant compositions, and particularly to heat stable compositions of this class.
Many type penetrants have in the past been used to locate flaws or discontinuities in metallic and non-metallic surfaces. The usual method of application is to apply the penetrant to the surface and after a suitable time the excess penetrant is removed by washing with a suitable solvent system or mechanically by wiping with a cloth or other absorbent material. Flaws are subsequently revealed by a seepage of the penetrant from the crevice or cavity. Various agents have been added to the penetrant to increase the visibility of the seepage. These include ordinarily visible dyes, and fluorescent dyes. Absorbent powders are often applied to the surface of the article to absorb some of the dye and thus to increase the visibility of the flaw.
Fluorescent type penetrants which are currently available tend rapidly to lose brightness on metal surfaces when exposed to temperatures greater than about 140.degree. F.; and typically such penetrants lose about 75% or more brightness in about 30 minutes. Accordingly, minute flaws or cracks in the metal surface can and do go undetected, in many cases due to rapid fading. The term "brightness" as used herein refers to visibility under ultraviolet light.